The present invention relates to thermal electro-static ink-jet recording, and particularly to such recording method using an ink which has physical properties appropriate for stablizing the thermal electrostatic ink-jet recording operation to prevent erroneous jetting of the ink, while operating at high speed.
Examples of conventional non-impact ink-jet recording apparatus include an apparatus in which electrostriction elements, such as piezzo-electric elements or the like, are provided in an ink chamber, and the ink pressure within the ink chamber is raised by applying a voltage of a predetermined frequency to the elements so that a drop of ink can be jetted from an orifice of the ink chamber.
Such non-impact ink-jet recording methods have advantages compared to impact recording methods in that noise is reduced during operation and a special process, such as of photographic fixing, is not required, because the recording is accomplished by deposition of ink droplets on paper.
However, conventional ink-jet recording apparatus has structural limitations, e.g., in miniaturizing the ink-jet mechanism of the ink chamber provided with the electrostriction elements. Further, it is difficult to obtain a predetermined pel density, and mechanical scanning is required. Accordingly, there are limitations on improving the printing speed. Furthermore, problems such as an ink-clogging of the orifice can occur.
To overcome such disadvantages, several kinds of ink-jet recording apparatuses, for example, (1) the magnetic ink-jet system, (2) the plane scanning ink-jet system, (3) the thermal bubble ink-jet system, (4) the electrostatic attraction ink-jet system, and others, have been proposed. The first, the magnetic ink-jet system, employs an array of magnetic electrodes disposed at intervals corresponding to pel density. The array is driven in response to a pel signal to generate a magnetic field so as to thereby form a meniscus structure of ink, and an electrostatic field is applied to the meniscus to jet ink. In the second, the plane scanning ink-jet system, a slit-like ink reservoir is provided in parallel to an array of electrodes disposed at intervals corresponding to pel density. An electric, field pattern corresponding to a pel signal is formed between the electrode array and an electrode disposed opposite the electrode array behind a recording paper. On the basis of the electric field pattern, ink is jetted from the ink reservoir. In the third, the thermal bubble ink-jet system, an array of heating elements is disposed at intervals corresponding to pel density so that ink is heated in response to an image signal to produce surface boiling (500.degree. to 600.degree. C.) to raise the pressure within an orifice so as to jet a drop of ink. In the fourth, the electrostatic attraction ink-jet system, ink is electrically attracted by an electric field created in response to an image signal. At the same time, a stream of air is applied to the ink to jet the ink.
The ink-jet recording apparatuses of the systems of the above first, third and fourth types have an advantage in that high-speed recording can be accomplished because the ink is jetted by the cooperative action of a magnetic field pattern (or electric field pattern) formed in response to an image signal and an electric field (or airflow). The ink-jet recording apparatus of the second of the above systems has the advantage of avoiding ink-clogging because an orifice for jetting the ink is not required.
However, these ink-jet recording apparatuses have disadvantages as follows. With the magnetic ink-jet system color imaging is difficult because magnetic material for magnetizing ink is contained in the ink. Because the signal voltage level should be high in the plane scanning ink-jet system, an electric field is often formed at a non-selected part of the array. Accordingly, there is a possibility of erroneous ink jetting. Furthermore, because resting time is long, the recording speed cannot be made sufficiently high. In the thermal bubble ink-jet system there is a possibility of shortening the lifetime of the heating elements because of cavitation caused by appearance and disappearance of air bubbles. In the electrostatic attraction ink-jet system, because the ink attraction voltage level should be high, it is difficult to integrate driving elements at intervals corresponding to pel density. Accordingly, when a matrix driving method is employed, the recording speed cannot be made sufficiently high.
In view of the aforementioned disadvantages of the above-mentioned ink-jet recorders, there has also been proposed a thermal electrostatic ink-jet recording apparatus superior in durability, in jetting accuracy, in color imaging, and in recording speed.
The latter thermal electrostatic ink-jet recording apparatus is effectuated through a process in which the surface tension, interfacial tension, viscosity, and electric resistance of electrically resistive or conductive ink are lowered to form a meniscus of ink, and an electric field is concentrated on the meniscus to thereby jet the ink from the orifice.
In this thermal electrostatic ink-jet recording apparatus, however, there is a possibility of erroneous jetting of ink from a non-heated part of the recording head, not in response to an image signal, when conditions inappropriate for jetting ink are set. Accordingly, a disadvantage is such that printing quality may deteriorate due to the erroneous ink jetting.